Smart Windows: Optical and Thermal Performance Evaluation
Abstract
A new concept for a Smart Window system is discussed, which can provide electricity and reduce solar gain by integrating high efficiency third generation photovoltaic cells with Fresnel lens concentrators that replace the active blinds currently employed in some double glazed facades. In the proposed window system, high efficiency concentrating photovoltaic elements (CPVs) are tracked in 2-axes to allow direct solar radiation incident at the glazing surface to be collected. The 2-D tracker is designed to avoid the overlapping and shading effects between adjacent Fresnel lenses. This design could also provide hot water or air obtained by cooling the cells for use within the building. In the optical analysis, beam intensity to the CPVs and room, diffuse intensity to the room through the window system, and radiation absorbed by the window components are analysed. Using the solar radiation fluxes calculated in the optical analysis TRNSYS based simulations of a simple building model located in Madrid and Birmingham were performed for rooms with standard double glazed and smart windows. Predicted zone temperatures and cooling loads resulting from solar gain show reduced peak room temperatures with cooling loads reduced by 40% annually for rooms with the smart window system.